The present invention relates to a tubular body made of FRP used for a golf club s haft, fishing rod, ski stick, frame of a bicycle and so forth.
In order to enhance the specific strength and the specific rigidity of a laminated body, for example, Japanese Unexamined Utility Model Publication No. 6-7923 discloses an arrangement of a body layer formed of fibers and resin, and a ratio of resin to a total of fibers and resin is 10 to 20 weight percents.
However, in the case of a tubular body such as a golf club shaft to which bending stress or torsional stress is applied and further an impact force is given when a golf ball is hit by the golf club, separation and damage tend to occur among the fibers and layers compo sing the shaft, or alternatively separation and damage tend to occur in a portion where parts are attached to the shaft.
It is an object of the present invention to provide a tubular body, the specific strength and the specific rigidity of which are high. It is Also an object of the present invention to provide a tubular body,the specific strength and the specific rigidity of which are high, and the tubular body is less susceptible to separation and damage even if an impact force is given to it.
In the tubular body of the present invention, a ratio of impregnation of synthetic resin in prepreg on the main body layer, which is a primary component, is determined to be in a range from a value not lower than 10 wt % to a value lower than 25 wt %. When the ratio of impregnation of synthetic resin in prepreg on the main body layer is determined to be in the above range, the characteristic of reinforcing fibers can be exhibited, so that a tubular body of high specific strength and specific rigidity can be provided.
In this case, when the main body layer is formed of layers of prepreg including skew fibers arranged in a skew direction and axial fibers arranged in an axial direction, blow holes are generated in synthetic resin on an interface between the skew fiber layer and the axial fiber layer. Due to the above blow holes, separation and damage tend to occur on the main body layer. When a thin layer, the ratio of impregnation of synthetic resin of which is high, is formed between these layers, both layers are made to adhere tightly to each other, and the occurrence of separation and damage can be prevented.
When the main body layer is formed of a layer of prepreg including skew fibers arranged in a skew direction and axial fibers arranged in an axial direction, in order to enhance the specific strength and the specific rigidity, the ratio of impregnation of synthetic resin contained in prepreg of each main body layer may be reduced. However, when the ratio of impregnation of synthetic resin contained in the skew fibers is excessively reduced, a sufficiently large quantity of synthetic resin can not be provided among the fibers and layers. As a result, separation tends to occur. Accordingly, when the ratio of synthetic resin impregnated in the skew fibers is reduced to a value at which separation is not caused and also when the ratio of synthetic resin impregnated in the axial fibers is more reduced than that, it is possible to provide a tubular body, the specific strength and the specific rigidity of which are high, and separation is not caused among the fibers and on the interface.
In order to enhance the specific strength and the specific rigidity, when the ratio of impregnation of synthetic resin in prepreg on the main body layer is reduced and a layer, the ratio of impregnation of synthetic resin of which is high, is provided in a predetermined region in the axial direction (a region to which an impact force is given), it is possible to provide a tubular body, the specific strength and the specific rigidity of which are high, and also the impact resistance of which is high.